<DE2> Volume + Instructions to update Song

On this commit:
1) Volume Control -- needs to test with merged code which I will be merging soon.
2) Instructions to update Song:
drawAllSongs() - draw all songs in song panel.
playSongFromSongPanel(int id) - highlight and play song with specified ID.
<DE2> Instruction to play song

I had a typo on the function name on previous commit.
Instructions:
drawAllSongs() and playSongFromSongPanel(int id)
Merge branch 'master' of https://github.com/Ilikecattle/EECE381Module2

Conflicts:
	software/StereoSystem/Button.c

Merging with Danny's changes.
<DE2> Fixed issue on Volume control

Volume will check if the db.songs[song_id]->sound is null or not.
If it is null, do nothing.